In the 3rd Generation Partnership Project (3GPP) that is a mobile communication system standardization project, introduction of a device-to-device (D2D) communication into Release 12 as a new function is under consideration (see Non Patent Literature 1).
In the D2D communication, a plurality of nearby user terminals perform direct inter-terminal communication without intervention of a network. Meanwhile, in cellular communication that is ordinary communication of a mobile communication system, user terminals perform communication via a network.